Fabricated welding wire for corrosive-resistant stainless

ABSTRACT

A fabricated electrode is disclosed in the form of an elongated or continuous metallic sheath, composed for example of cold-rolled mild steel, and containing specific components somewhat uniformly distributed along its length, and for use in shielded-arc welding. Specifically, the composite provides a stainless steel and includes: a major percentage of iron; a limited amount, however, at least about 09.00 percent by weight of alloying metal, e.g. chromium; from about 0.01 to about 0.08 percent by weight of carbon and further including titanium in an unconventionally large amount .[.of at least about six times the percentage by weight of the carbon in the composite.].. Advantages are disclosed for the provision of the titanium in the form of ferrotitanium, and the chromium in the form of ferrochromium, a major portion of which has a small particle size. Also as disclosed, the composite further includes deoxidizing agents, e.g. manganese and silicon.

This is a continuation of application Ser. No. 402,440, filed Oct. 1,1973, now abandoned.

BACKGROUND AND SUMMARY OF THE INVENTION

From time to time the need arises for a welding wire or continuous arcelectrode that is usable to weld alloys having rather specificcharacteristics. The situation is exemplified by a need that existed inrelation to catalytic converters for automotive use and other hightemperature anti-pollution devices. Specifically, proposals have beenmade to reduce the volume of air pollutants from automotive engines bycatalytic converters that process the engine exhaust stream. One of thedifficulties encountered in the course of developing a commerciallypractical catalytic converter relates to the highly-corrosive nature ofthe exhaust stream. A solution to that problem involves the use ofcorrosive-resistant, though relatively inexpensive stainless steelalloys, notably Type 409M stainless steel.

Although Type 409M stainless steel is very resistant to corrosion, andrelatively inexpensive, it also is substantially nonductile.Consequently, the use of the material in fabricated structures haspreviously been quite limited and efforts to draw welding wire for thematerial presents considerable problems. Specifically, forming weldingwire from such alloys directly is not feasible because the material isnot sufficiently ductile to be drawn. That is, a billet of 409Mstainless steel would require formation into a wire for effective use inarc welding processes. The problems attendant forming a billet of suchalloy into a usable wire are strongly compelling against pursuing such aprocess.

The difficulty of forming welding wires, as from billets of 409Mstainless, suggested the possibility of fabricating wire electrodes.Accordingly, wires were fabricated to contain components of an alloy aswould be expected to form a satisfactory weld. However, repeated testswith such wires have been unsatisfactory. Substantial efforts tomaintain the weld of sufficient strength, and outside the gamma loop(region of hardening), generally have been successful only with wires ofrelatively very high cost.

In general, the present invention is directed to an economical wire andprocess for effectively welding 409M stainless steel, which wire is inthe form of a fabricated electrode, e.g. metallic strip formed into asheath so as to enclose other desirable components for the compositewire. A characteristic of the fabricated wire of the present inventionis that it forms a weld deposit that falls outside the gamma loop whilecontaining a practical quantity of carbon for strength. The wire isattained, recognizing the economic significance of using relatively low(under 14% or 15% by weight) quantities of chrome. In the combination ofcomponents as defined and considered below, the need was discovered foran unconventionally very-large quantity of titanium to produce anelectrode that may be effectively employed in gas-shielded arc welding.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT

As required, detailed illustrative embodiments of the invention aredisclosed herein serving in that regard as the best modes presentlycontemplated. The embodiments exemplify the invention which may, ofcourse, be constructed in various other forms, some of which may beradically different from those disclosed herein. However, the specificdetails disclosed are representative and provide a basis for the claimswhich define the scope of the present invention.

Further in the above regard, it is noteworthy that welding electrode orwire in accordance herewith can be fabricated by any of several wellknown and commercially-employed processes. Essentially, the fabricationinvolves enclosing a core of selected particulate materials in a metalsheath so that the core is effectively contained and isolated. The basicproduction techniques involved in such fabrication are disclosed, forexample, in U.S. Pat. Nos. 1,629,748 and 1,640,859, issued to W. F.Stoody. However, the fabrication process has been the subject of manyrefinements and as indicated above is well known so that furtherdetailed description herein is neither deemed appropriate nor necessary.It is pertinent that advantages result from the use of cold-rolled mildsteel in the fabrication of wire in accordance with the presentinvention. The advantages include: economy, ease of fabrication and theavailability of such material.

The metallic components of electrodes as disclosed and considered hereinare normally obtained from both the sheath material and the particulateor pulverized metals and alloys contained therein. As suggested above,mild steel, e.g. having a maximum carbon content of 0.10 percent byweight, is accommodating as a sheath for the contents of the compositeelectrode. Of course, it is recognized that a wire may be fabricated inaccordance with the present developments, using sheaths of various othermetals or alloys.

With regard to another component of the wire, the quantity of chrome hasbeen determined to be at an effective though economic amount at betweenabout 10.0 and 14.0 percent by weight. In that regard, distinctadvantages are recognized for the use of ferrochromium in the compositeelectrode. Specifically, ferrochromium is relatively easy to crush to afine particle size and it has been found desirable to reduce the majorportion of the core to particles that are no larger than 40 mesh size.Furthermore, the use of ferro-chrome affords effective distribution ofthe chrome throughout the core. That is, as the chrome is somewhat-lessconcentrated by its presence in ferrochrome, a more uniform distributionof chrome throughout the core is accomplished in the fabricated wire.

In relation to the titanium present in the wire, it is to be recognizedthat pure titanium is unstable and rather difficult to handle. By usingferrotitanium to provide the requisite titanium in the composite,handling is simplified, greater quantities are recovered in the deposit,and the uniformity of distribution is also improved. Of course, in viewof the lesser quantity of titanium in the composite, improveddistribution and greater uniformity is perhaps even of greatersignificance than in the case of the chrome. In general, it has beenfound desirable to utilize a ferro-titanium which contains not more than80 percent titanium.

Wires formed in accordance herewith may be effectively employed asconsumable electrodes in gas-shielded arc-welding processes. That is,the electrode is electrically energized to provide an arc and as theelectrode enters the electric arc, from which a weld deposit is formed,the arc is shielded by gas, e.g. argon or hellium, to limit oxidationtherein substantially as described in the WELDING HANDBOOK (Section Two)entitled Welding Processes, Fifth Edition, published by American WeldingSociety, 1963.

Other details, objects, characteristics and advantages of welding wiresconstructed in accordance with the present invention will becomeapparent in view of the following description of certain specificembodiments.

EXAMPLE 1

In considering a formulation for arc welding 409M stainless, it wasdetermined that a significant amount of carbon was required for adequatestrength, e.g. at least 0.01% by weight. However, significant amounts ofcarbon tended to result in a non-ferritic weld deposit. The addition ofconventional amounts of titanium, e.g. up to four times the quantity ofthe carbon present were not effective to accomplish a ferritic deposit.Wires of high chromium content were suggested; however, economicconsiderations urge against such formulations.

Ultimately, it was discovered that an unconventionally large quantity oftitanium was required to attain the desired characteristics for thedeposit. It is theorized that the need for such quantities of titaniumarises due to titanium loss in crossing the arc of a fabricated rod.That is, as the fabricated rod contains some air (containing oxygen) aswell perhaps as some spurious oxides, the titanium oxidizes regardlessof the effectiveness of any shield, e.g. gas enclosure.

On the basis of tests, subsequent to the discovery of a need for anunconventionally large quantity of titanium, a welding wire or electrodefor welding 409M stainless steel was fabricated using a low-carbon (0.10maximum) mild steel strip as a sheath. The sheath comprised about 78.8percent by weight of any given length of the wire. That is, the wire wasformulated to have a substantially-uniform composition over any lengthof reasonable size and the sheath comprised about 78.8 percent by weightof the length. .Iadd.78.8%·0.10% carbon=0.079% carbon .Iaddend.

The core contained within the space defined by the sheath included:ferrochromium 16.5 percent by weight (70 percent chrome content);ferrotitanium 3.2 percent by weight (30 percent titanium); ferrosilicon0.9 percent by weight and manganese metal 0.6 percent by weight..Iadd.3.2%·30%=0.96% titanium .Iaddend.

The component ingredients of the core were provided in a particle formwith the major amount thereof being reduced to particle sizes not largerthan 40 mesh. Within the capability of current commercial productiontechniques, the core ingredients then were uniformly distributed withinthe sheath in accordance with the percentages set forth above.

In operation, the wire was effective to arc weld (argon shielded) 409Mstainless steel, producing a weld having an analysis substantiallysimilar to the base metal. Welds accomplished with the wire wereeffective and of good quality, having good strength and no apparentcracks or defects.

EXAMPLE 2

Wires substantially as set forth above also were formulated withvariations in the amount of carbon. In that regard, several wires wereformulated, in which the amount of titanium present was at least sixtimes the quantity of the carbon present but not over 3% of the wire, ineach case on the basis of weight. Each such wire was effective for usein arc welding 409M stainless with a gaseous shield as known.

It is to be recognized that an amount of titanium equal to only sixtimes the amount of carbon (by weight) involves a very-tightly packedwire, containing very little air or spurious oxides. For wires ofincreased oxygen content, an increased quantity of titanium will benecessary to obtain an effective ferritic weld deposit. ##EQU1##

Although relatively high quantities of titanium are usable, of course,economic considerations favor the use of minimally-effective quantities.

EXAMPLE 3

Finally, experiments were undertaken to formulate the practical andeffective limits for .Iadd.other .Iaddend.component ingredients of theelectrode. In that regard, several wires were fabricated and tested andthe economic aspects were analyzed. As a consequence, the following isset forth as defining ranges for each ingredient to obtain a commercialwelding wire or electrode in accordance herewith that may besuccessfully used in gas-shielded arc welding processes to weld 409Mstainless. Specifically:

    ______________________________________                                        Ingredient     Percentage by Weight                                           ______________________________________                                        carbon         between about 0.01 and 0.08                                    manganese      between about 0.40 and 1.00                                    chromium       between 09.0 and 14.0                                          silicon        between about 0.4 and 1.0                                      .[.titanium    at least six times the weight.].                                              .[.percentage of carbon present.].                             sulfur         up to 0.03                                                     phosphorus     up to 0.03                                                     iron           between about 73.55 and 89.50                                  ______________________________________                                    

In the defined ranges and as set forth above, iron is the majorcomponent. Carbon is present to afford the requisite strength andhardening. Manganese and silicon are present as deoxidizers or wettingagents for the welding operation in amounts that are somewhatcharacteristic. Chromium is present to accomplish the desired alloy yetis limited to an economic quantity. Titanium is present as consideredabove in detail.

As indicated above, electrodes formulated within these definitions havebeen determined to be economically feasible and to consistently produceeffective welds on 409M stainless steel. Accordingly, these rangesafford the basis for the claims as set forth below to define the scopeof the present invention.

What is claimed is:
 1. An arc-welding electrode comprising:an elongatedmetallic sheath defining an internal space; particulate material in saidspace of said sheath; said sheath and said material in composite alongthe length of said sheath consisting essentially of a major percentageof iron, between about 9.0 and 14.0 percent by weight of chromium, fromabout 0.01 to about 0.08 percent by weight of carbon, an effectiveamount of deoxidizer material, up to 0.03 percent by weight each ofsulfur and phosphorous, and further including titanium in the form offerrotitanium having less than 80 percent by weight of titanium but anamount at least .[.six.]. .Iadd.twelve .Iaddend.times the percentage byweight of said carbon in said composite and not in excess of 3% byweight of said electrode, a major portion of said ferrotitanium beingreduced to a size not larger than 40 mesh.
 2. An electrode according toclaim 1 wherein said chromium is present in the form of ferrochromium.3. An electrode according to claim 1 further in which said deoxidizingmaterial is in the form of manganese and silicon.
 4. An electrodeaccording to claim 3 wherein said silicon and manganese are each presentin an amount of between about 0.40 and 01.00 percent by weight.
 5. Anelectrode according to claim 1 wherein said metallic sheath comprisescold-rolled mild steel.
 6. An electrode according to claim 5 in whichsaid deoxidizing ingredients are in the form of manganese and silicon inwhich said silicon and manganese are each present in an amount ofbetween about 0.40 and 01.00 percent by weight.
 7. In a process forforming a stainless steel weld on a workpiece wherein an arc weldingelectrode is electronically energized to provide an arc between saidwelding electrode and said workpiece and wherein said arc is shieldedwith a gaseous shield to limit oxygen therein, said electrode consistingof an elongated mettalic sheath defining an internal space andparticulate material in said space of said sheath, the improvementaccording to which sheath and said material in composite along thelength of said sheath consists essentially of a major percentage ofiron, between about 9.0 and 14.0 by weight of chromium, from about 0.01to about 0.08 percent by weight of carbon, an effective amount ofdeoxidizer material, up to 0.03 percent by weight of sulfur andphosphorous, and further including titanium in the form of ferrotitaniumhaving less than 80 percent by weight of titanium but an amount at least.[.six.]. .Iadd.twelve .Iaddend.times the percentage by weight of saidcarbon in said composite and not in excess of 3% by weight of saidelectrode, a major portion of said ferrotitanium being reduced to a sizenot larger than 40 mesh.